High power loads are often used as terminations on the isolated port of a circulator. The circulator then becomes an isolator which can be used to protect transmitters and receivers from damage due to reflected signals. Such signals are ported to the termination on the isolator where they are absorbed. Some isolator applications also include DC bias currents superimposed on the RF line. The bias does not present a problem for the circulator. However, the circulator termination will sink the bias current. This sinking results in unnecessary continuous DC power consumption, and requires that the termination be rated to absorb the additional energy. One solution to this problem is to include a blocking capacitor in series with the termination. The capacitor passes the RF signal to the load, but not the DC bias.
Blocking capacitors may be connected to the loads in a variety of configurations. Most require the purchase of an additional part, accommodation on the circuit board or housing for the part, and finally the labor required for the installation of the part. If the capacitor can be incorporated into the load without adding significantly to the load cost, then much of the cost associated with the additional part can be saved. The capacitor must have a breakdown voltage suitable for the application, and must operate as a low impedance device over the frequency of operation of the circulator. If the termination is constructed so that the capacitor is situated between the load and the RF ground, then the breakdown voltage requirement for the RF signal is low.